Letting Mississippi run its natural course could save New Orleans from hurricanes

The full diversion of the Mississippi River back down the Atchafalaya basin would flood millions of acres, permanently submerge entire communities, destroy oil refineries and farms, and leave the port of New Orleans without its river. But it could also save Louisiana from the next hurricane.

ByWilliam SargentMay 19, 2011

Ipswich, Mass. — During the next few days the Army Corps of Engineers must continue making their Hobbesian choice between the ultimate disaster for New Orleans and an $18 billion bet that they can beat Mother Nature. To keep flood waters from breaking the levees and charging into the city, the Corps is making an $18 billion gamble that they can divert a fourth of the Mississippi’s flow down the Atchafalaya River without losing control of the situation.

The choice may seem obvious, but the Corps’ gamble also holds potentially devastating consequences for New Orleans. If it loses control of the diversion, the entire flow of the Mississippi could suddenly come thundering down the Atchafalaya – the course nature wants it to follow – never to be diverted back. Farms, towns, and oil refineries would be drowned, and the key port cities of New Orleans and Baton Rouge would be left without their river.

As the Corps begins the partial diversion of the Mississippi down the Atchafalaya, coastal scientists should seize on the opportunity to consider longer-term shifts in the river’s course. It’s possible that this crisis could lead to a less costly and more sustainable way of dealing with the problems of coastal Louisiana.

Although such a shift in the river’s path would deal a devastating economic blow to the region, allowing the Mississippi to flow west down the Atchafalaya would ultimately be in the best long-term ecological interest of the area because it would build up the southern Louisiana coast as a buffer against future hurricanes.

New Orleans: a city under a river

The Mississippi River is impressive. In New Orleans, it is straitjacketed between 20-foot high levees, and the river itself is over 150 feet deep. When President Bush finally went down to New Orleans to address the situation after hurricane Katrina, he stood on Jackson Square, facing the river that flowed by, 20 feet over his head.

You could see the superstructure of supertankers and hear the quiet thrumming of their engines as they cruised by in front of him. If the ships could have cruised over the nearby superdome they would have hovered in the air 10 feet above centerfield. It would have been an impressive photo-op, indeed, if the levees had decided to break during the presidential address.

New Orleansians consider the breaking of the river levees to be the ultimate disaster that could befall their city. The full force of the Mississippi would fill up the underwater bowl in which New Orleans lies with far more force and water than filled the city when Lake Pontchetrain burst it’s levees after Katrina. The last time that almost happened was during the great flood of 1927. As rain fell and flooding developed at an alarming rate, New Orleans businessmen convinced the federal government to dynamite the levees in nearby Plaquemines Parish to avoid further drowning the city

As it turned out, breaking the levees submerged and destroyed all of Plaquemines Parish, leaving over 6,000 people homeless, though each was given the unseemly paltry sum of $169 each for his losses.

Like trying to hold back the tide

It is obvious the Army Corps of Engineers could not let such a disaster happen again. They have already opened the Bonnet Carre spillway, which is now bleeding muddy Mississippi waters into Lake Pontchetrain, just north of the city. And as flood waters continue to rage and the prospect of future flooding looms large for the city, New Orleans residents worried: Was such a diversion enough? But the Corps had an $18 billion trick up its sleeve.

For thousands of years, the Mississippi River has naturally writhed back and forth like a water hose, spewing muddy sediment loads first one place then another along several hundred miles of coast. These movements built up a number of major deltas along the southern Louisiana coast.

This shifting geography has gradually reoriented the course of the river. Now the river is running about as far east as it can possibly go, and it wants to writhe back west, away from New Orleans and down the Atchafalaya River Basin instead.

But in the late 1950’s, Congress passed a bill to save the port of New Orleans by making it illegal for more than a third of the Mississippi to flow down the Atchafalaya River basin. This is akin to passing a bill to hold back the tide.

A tale of two rivers

Today, the equivalent of seven Niagara Falls tumbles down from the Mississippi into the Atchafalaya River, making the Atchafalaya the second largest river in the country. A gunboat patrols the area in case some barge breaks loose and crashes into the dam holding back the two torrents, which desperately want to embrace. In 1937, the dam almost broke, sending engineers screaming into the night. The dam shook so severely that coal in a nearby railroad car ignited from the vibrations. After the flood, engineers discovered the river had scoured out a 100-foot deep hole in the water at the foot of the dam.

Since then, the Army Corps has made an $18 billion bet that they can prevent such a break – and the unplanned disastrous flooding that would follow – from happening again. The dice were thrown last Saturday when the Corps started carefully opening the Morganza Spillway to relieve pressure both on the levees of New Orleans but also on the old river control structure that separates the two rivers. The plan is to continue opening the spillways gate by gate until close to a quarter of the flow of the Mississippi flows down the Atchafalaya.

In doing so, they will intentionally flood what was originally projected to be around 3 million acres of land in a swath that would almost reach from Boston to New York City. It would be like flooding the state of Connecticut under 5 to 25 feet of water. A dozen communities and two small cities will be inundated, along with 11 major oil refineries. Citizens of the area have already moved to higher ground.

An even greater calamity

But the danger in the Corps’ bid to control Mother Nature could result in even greater calamity. The Corps could lose control of the situation and all of the mighty Mississippi could burst the old river control structure, and the full force of the Mississippi could come barreling down into Atchafalaya, never to return to its original course.

This would leave both New Orleans and Baton Rouge – key port cities – without their rivers. Billions of dollars in infrastructure and commerce would be lost, and America’s petrochemical industry would be dealt a devastating blow. Eventually, the Gulf of Mexico would flow back up the empty Mississippi river basin toward New Orleans and Baton Rouge, with unforeseen consequences.

Why no river for New Orleans might save it

But such a shift could ironically serve the long-term ecological interests of the region. Allowing the Mississippi to follow its natural course down the Atchafalaya would devastate cities, farms, and oil refineries, but it would also offer the region some long-term protection.

The Mississippi sediments that now flow uselessly into the depths of the Gulf of Mexico would start to rebuild the marshes of Southern Louisiana, creating a coastal barrier against future storms. Marshes are nature’s way of protecting coasts from hurricanes, and New Orleans knows the costs of hurricanes like Katrina all too well.

Marshes are Nature’s way of protecting coasts from hurricanes. Every mile of marsh brings down storm surges from hurricanes by a foot. If the marshes of southern Louisiana had been allowed to grow naturally, it’s fair to say that New Orleans would not have been flooded by hurricane Katrina. Coastal scientists should continue watching to see if this crisis will offer ideas for how to rebuild Louisiana’s marshes – even if that means allowing the Mississippi to change its course.